1. Field of the Invention
Particularly the present invention relates to a magnetic sensing element which reduces asymmetry with improved stability of magnetization in a free magnetic layer, thus enabling improvement in stability of reproducing characteristics including noise suppression.
2. Description of the Related Art
In a tunneling magnetic sensing element, for example, a hard bias layer extends at both sides of an element portion which exhibits a tunneling magnetoresistance effect.
The hard bias layer applies a bias magnetic field to a free magnetic layer being one component of the element portion, thereby improving the stability of magnetization in the free magnetic layer.
The hard bias layer is required to be so stable that the hard bias layer itself will not cause a change in magnetization in response to an external magnetic field and also be capable of applying a large bias magnetic field to the free magnetic layer.
Japanese Unexamined Patent Application Publication Nos. 08-50709 and 08-287419 are examples of the related art.
It is desirable that the hard bias layer is large in both coercive force Hc and Mr×t (Mr is residual magnetization; t is film thickness). The coercive force Hc mainly contributes to the stability of the hard bias layer with respect to the external magnetic field, while the Mr×t mainly contributes to the magnitude of the bias magnetic field with respect to the free magnetic layer.
However it has been difficult to increase both the coercive force Hc and the Mr×t of the hard bias layer. For instance, increasing the coercive force Hc by selecting the material of the hard bias layer resulted in decreasing the Mr×t.
Accordingly, heretofore the stability of magnetization in the free magnetic layer was insufficient and therefore the asymmetry increased, so that the stability of reproducing characteristics could not be sufficiently improved, e.g., resulting in increasing noise.
In the above-identified Patent Documents, the hard bias layer has a layered structure. However, these Patent Documents do not aim at increasing both the coercive force Hc and the Mr×t of the hard bias layer that is to apply a bias magnetic field to the free magnetic layer. Moreover, they do not define essential magnetic properties, concrete film thicknesses and so on of upper and lower hard bias layers.